Plyometric training techniques often require that a weighted bar be pushed away by a trainee from a starting position as quickly as possible by the trainee. It is sometimes desirable that the trainee push the bar beyond the trainee's grasp; the bar is then typically captured by the trainee in a gravity-directed return movement of the weighted bar toward the starting position. The trainee may thereby be placed in the pathway of the returning bar and can run a risk of injury by the returning bar.
Plyometric muscular training is used to increase absolute muscle strength in numerous physical training and therapeutic programs. In particular, the development of explosive strength affected by plyometric muscular training is important for most sports. This ability is difficult to increase with conventional peak-contraction training methods wherein the fully contracted muscle is maintained in continuous tension.
When a concentric contraction occurs immediately following an eccentric contraction, then the force generated can be dramatically increased. This increase in force is lost if the eccentric contraction is not followed immediately by a concentric effort. To express this greater force the muscle must contract within the shortest time possible. This whole process is frequently called the stretch shortening cycle and is the underlying mechanism of plyometric training. Plyometric training places increased stretch loads on the working muscles. As the muscles become more tolerant to the increased loads, the stretch-shortening cycle becomes more efficient.
A muscle develops its maximum force during a rapid eccentric contraction. An “eccentric contraction” occurs when a muscle is forced to lengthen due to the high external load, although it may be fully activated. “Contraction” in this context does not necessarily imply shortening. Contractions that permit the muscle to shorten are referred to as “concentric contractions.” In concentric contractions, the force generated by the muscle is always less than the muscle's maximum. Of course, muscles seldom perform one type of contraction in isolation during athletic movements.
A bilateral deficit can also be addressed by plyometric muscular training techniques. The bilateral deficit is the difference between the maximal effort that can be developed with one arm (or leg) and two arms (or legs) working together. For example, persons generally cannot exert a force during a two-arm effort that is twice that of the one-arm maximal effort.
Plyometric training techniques can be used to increase physical fitness, enhance athletic skills, and improve mobility in a wide range of persons. There is, therefore, a long felt need to provide devices and methods that safely make the benefits of plyometric muscular training techniques to a wide range of people.